(1) Field of the Invention
The present invention relates to blood dialysis. More specifically, this invention is directed to automatically producing dialysis fluids and transporting such fluids through a dialysis device. Accordingly, the general objects of the present invention are to provide novel and improved methods of such character.
(2) Description of the Prior Art
While not limited thereto, the present invention is especially suited for use with blood dialysis devices such as artificial kidneys. As is known, an artificial kidney includes a vessel which is separated by a semi-permeable membrane into at least a pair of zones through which a dialysis fluid and the blood of the patient respectively flow. The electrolytes and other substances to which the membrane is permeable are exchanged through the membrane during the cleansing or dialysis operation; the exchange occurring in both directions through the membrane. The speed of exchange of the dilutents in the solutions on either side of the dialysis membrane or membranes is largely dependent on the differences of the concentrations of the dilutents on the different sides of the membrane. The passage of water through the dialysis membrane, however, is primarily dependent on the pressure differential thereacross. Thus, the amount of water which passes through the dialysis membrane during a treatment procedure is dependent on the total trans-membrane pressure; this pressure being dependent on the pressure drop between the blood and dialysis fluid flow zones and upon other pressure factors. The pressure dependent passage of water through a dialysis membrane is a phenomenon known in the art as ultra-filtration. The degree of ultra-filtration is a critical factor in the treatment of uremic patients.
It is of extreme importance that the values of the trans-membrane pressure, the concentration of the dialysis fluid and the rate of flow of the dialysis fluid be maintained constant during an entire treatment procedure, which normally takes between six and ten hours, in order to insure that a specific predetermined amount of ultra-filtration and exchange of dilutents will occur. Thus, in order to insure a reliable dialysis, an artificial kidney is provided with a control system for the purpose of regulating the dialysis fluid concentration and temperature. Artificial kidney control systems also include a blood leak detector and various devices which seek to maintain the desired trans-membrane pressure.
Blood dialysis techniques as generally described above are known. Presently available types of dialysis equipment, however, share the common disadvantage that the dialysis fluid flow quantity is variable for a selected trans-membrane pressure. Accordingly, available dialysis equipment is provided with overflow systems and continually over produce the dialysis fluid whereby part of the fluid goes directly into waste drainage via the overflow system. The over production of the dialysis fluid guarantees an adequate supply during the dialysis. Since the overflow is at ambient pressure, drainage into a rinsing pan at normal height is impossible; i.e., it is necessary that the drainage downstream of the dialysis device be positioned lower than the overflow level.
A further disadvantage of presently available dialysis equipment and techniques resides in the requirement of an inlet water pressure which is at least 0.2 to 0.3 atmospheres above ambient pressure. There are many situations, for example during summer months on the upper floors of high rise buildings, where sufficient water pressure may not be available and thus the dialysis equipment will not function.
A still further disadvantage of presently available dialysis equipment is that the dialysis fluids can be produced only through setting a constant water/concentrate ratio.
It is advantageous, in order to guard against a component malfunction, to bypass the dialysis fluid through an internal bypass tube rather than to stop the fluid flow. Some of the available dialysis equipment includes bypass systems. These bypass systems, however, have an inherent defect from a safety viewpoint since, in the case of a defective valve, the dialysis fluid will continue to flow through the device or through the bypass without control.